Apparatus and method for mounting a hard pellicle

ABSTRACT

An apparatus for mounting at least one hard pellicle to a mask which includes an enclosure having an interior cavity, demounting means for removing a protective cover from a mask, mounting means for mounting at least one hard pellicle to the mask and conduit means for pumping a light-transmitting gas into the interior cavity between the hard pellicle and the mask.

FIELD OF THE INVENTION

[0001] The present invention generally relates to an apparatus and amethod for photolithography and more particularly, relates to anapparatus and a method for mounting a hard pellicle to a mask such thatthe mask can be readily installed in a projection mask aligner.

BACKGROUND OF THE INVENTION

[0002] A pellicle is a piece of transparent material mounted at adistance from the absorber surface on a reticle in the direction of thewafer. The distance is chosen to be out of focus from the wafer, so thatany foreign particles fallen on the surface of the pellicle is out offocus on the wafer, thus not contributing to printing defects.

[0003] The thickness of a pellicle is preferred to be small so that itspresence in the optical path does not affect the performance of theimaging lens. It is usually in the order of a few micrometers.Therefore, only polymer films can be found to have satisfactory opticaland mechanical properties for pellicle materials. Polymer materials havebeen available as the imaging wavelength was reduced from 436 to 365,248 and 193 nm.

[0004] When the imaging wavelength is further reduced to 157 nm, thereis difficulty in developing a thin and durable soft material that hassufficient light transmission. One has to use pellicles which is muchthicker and rigid. With a thickness sufficient to satisfy the mechanicalrequirement, it is already affecting the imaging property of the lens.Therefore, the flatness, smoothness and parallelism of a thick pelliclehave to be of high optical quality, making it very expensive.

[0005] Another drawback in using either soft or hard pellicles in 157 nmlithography is the requirement of an oxygen-free transmission space. Theentire optical path in a 157 nm imaging tool is flushed with high-puritynitrogen to prevent oxygen from getting into it. The pellicle either hasto permanently seal nitrogen in its enclosed volume with the mask or hasto allow for quick replacement of air with nitrogen when it is loaded inthe imaging tool. Either case is not easy to implement.

[0006] It is therefore an object of the present invention to provide amask that is protected by a pellicle which does not have the drawbacksor shortcomings of the conventional mask/pellicle assembly.

[0007] It is another object of the present invention to provide anapparatus for mounting a hard pellicle to a mask wherein the hardpellicle has optical transmission properties at least those of quartz.

[0008] It is a further object of the present invention to provide anapparatus for mounting a hard pellicle to a mask in an environmentfilled with a light-transmitting gas so that the interior cavity betweenthe mask and the hard pellicle is light-transmitting.

[0009] It is still another object of the present invention to provide anapparatus for mounting two hard pellicles to a mask with one on eachside of the mask.

[0010] It is still another object of the present invention to provide anapparatus for mounting at least one hard pellicle to a mask whichincludes delivery means for delivering the at least one hard pelliclecovered mask to a scanner.

[0011] It is yet another object of the present invention to provide animproved projection mask aligner in which a mask having a protectivehard pellicle mounted thereon is positioned in-between a light sourceand an imaging lens.

SUMMARY OF THE INVENTION

[0012] In accordance with the present invention, an apparatus and amethod for mounting at least one hard pellicle to a mask are disclosed.

[0013] In a preferred embodiment, an apparatus for mounting at least onehard pellicle to a mask is provided which includes an enclosure havingan interior cavity sufficiently large to accommodate a mask, an inletport for receiving a mask with a protective cover mounted thereon, andan outlet port for outputting a mask covered by at least one hardpellicle; demounting means for removing the protective cover from themask; mounting means for mounting the at least one hard pellicle on themask forming a hard pellicle/mask assembly; and conduit means forreceiving a light-transmitting gas and filling the interior cavity withthe light-transmitting gas.

[0014] The apparatus for mounting a hard pellicle to a mask may furtherinclude delivery means for delivering the at least one hard pelliclecovered mask to a scanner. The light-transmitting gas may be a gas thattransmits at least 70% of a light that has a wavelength smaller than 200nm, the light-transmitting gas may be an inert gas selected from thegroup consisting of N₂, Ar and He. The mounting means may includemechanical clamps, and may include mounting a first hard pellicle on themask juxtaposed to a surface having a layer of chrome coating. Themounting means may further include mounting a second hard pellicle onthe mask juxtaposed to a surface opposite to the surface that has thelayer of chrome coating. The at least one light-transmitting gas may bean inert gas selected from the group consisting of N₂, Ar and He. Theapparatus may further include a plurality of spacers of predeterminedthickness mounted in-between the at least one hard pellicle and themask. The apparatus may further include hard pellicle storage means,mask storage means, or hard pellicle/mask assembly storage means.

[0015] The present invention is further directed to an improvedprojection mask aligner of the type in which a mask having a protectivecover mounted thereon is positioned in-between a light source and animaging lens for projecting an image on a photoresist coatedsemiconductor wafer in order to form microelectronic circuits on thesemiconductor wafer, wherein the improvement includes a hard pelliclemounting apparatus that is positioned juxtaposed to the projection maskaligner for delivering a hard pellicle/mask assembly into the projectionmask aligner, the hard pellicle mounting apparatus further includes anenclosure that has an interior cavity sufficiently large to accommodatea mask, an inlet port for receiving a mask with a protective covermounted thereon, and an outlet port for outputting a mask covered by atleast one hard pellicle; demounting means for removing the protectivecover from the mask; mounting means for mounting the at least one hardpellicle on the mask forming a hard pellicle/mask assembly; and conduitmeans for receiving a light-transmitting gas and filling the interiorcavity with the light-transmitting gas.

[0016] In the improved projection mask aligner, the aligner furtherincludes a delivery means for delivering the hard pellicle/mask assemblyinto the projection mask aligner. The light-transmitting gas is a gasthat transmits at least 70% of a light that has a wavelength smallerthan 200 nm. The mounting means may include mechanical clamps. Thelight-transmitting gas may be an inert gas that is selected from thegroup consisting of N₂, Ar and He. The at least one hard pellicle mayhave optical properties at least that of a quartz lens. The alignerfurther includes a plurality of spacers of predetermined thickness thatare mounted in-between the at least one hard pellicle and the mask.

[0017] The present invention is further directed to a method for imagingwafers using a projection mask aligner which can be carried out by theoperating steps of first providing a projection mask aligner equippedwith a hard pellicle mounting apparatus, the hard pellicle mountingapparatus further includes an enclosure that includes an interior cavitysufficiently large to accommodate a mask, an inlet port for receiving amask with a protective cover mounted thereon, and an outlet port foroutputting a mask covered by at least one hard pellicle; demountingmeans for removing the protective cover from the mask; mounting meansfor mounting the at least one hard pellicle on the mask forming a hardpellicle/mask assembly; and conduit means for receiving alight-transmitting gas; forming a hard pellicle/mask assembly that hasat least one hard pellicle mounted thereon; positioning the hardpellicle/mask assembly in-between a light source and an imaging lens;positioning a photoresist coated semiconductor wafer under the imaginglens with a photoresist layer facing the lens; and imagingmicroelectronic circuits on the hard pellicle/mask assembly onto thesemiconductor wafer.

[0018] The method for imaging wafers using a projection mask aligner mayfurther include the step of flowing a light-transmitting gas into andfilling the interior cavity of the enclosure. The method may furtherinclude the step of forming the hard pellicle/mask assembly by clampingat least one pellicle to the mask by mechanical means. The method mayfurther include the step of supplying the at least one hard pellicle ina material that has optical properties at least that of quartz. Themethod may further include the step of storing the at least one hardpellicle in the hard pellicle mounting apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] These and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionand the appended drawings in which:

[0020]FIG. 1 is a cross-sectional view of a preferred embodiment of thepresent invention hard pellicle/mask assembly with a single pelliclemounted on the mask.

[0021]FIG. 2 is a cross-sectional view of an alternate embodiment of thepresent invention hard pellicle/mask assembly with two hard pelliclesmounted on both sides of the mask.

[0022]FIG. 3 is a cross-sectional view of a scanner equipped with thepresent invention hard pellicle mounting device wherein a single hardpellicle is mounted.

[0023]FIG. 4 is a cross-sectional view of a scanner equipped with thepresent invention hard pellicle mounting device wherein two hardpellicles are mounted to a mask.

DETAILED DESCRIPTION OF THE PREFERRED AND ALTERNATE EMBODIMENTS

[0024] The present invention discloses an apparatus for mounting atleast one hard pellicle to a mask wherein the apparatus may be attachedto a projection mask aligner (or scanner). The invention furtherdiscloses an improved projection mask aligner in which a hard pelliclemounting device is mounted to the side of the projection mask alignerfor installing at least one hard pellicle on a mask and then deliveringthe hard pellicle/mask assembly into the aligner.

[0025] One of the benefits made possible by the present invention novelapparatus is to reduce the cost of hard pellicles without sacrificingthe imaging performance. Another benefit made possible by the presentinvention novel apparatus is the inherent replacement of air by anon-light-absorbing gas, i.e., a light-transmitting gas, in the spacebetween the hard pellicle and the mask.

[0026] The benefits of reducing the cost of hard pellicle and the rapidreplacement of air by a light-transmitting gas can be achieved byinstalling a lens-quality thick pellicle in a pellicle preparation spacethat is already flushed with a non-light-absorbing gas. The space can bein the imaging tool itself or can be linked to the imaging toolenvironmentally. Prior to the use of the imaging tool, the mask can beprotected with a cover that may not transmit the actinic light. When themask is needed for exposure, the protective cover is removed in thepellicle preparation space, i.e. in the interior cavity of the presentinvention novel hard pellicle mounting device, and then the hardpellicle of optical quality is mounted on the mask. The hardpellicle/mask assembly is then sent to the reticle holder in the imagingtool.

[0027] Referring initially to FIG. 1, wherein a cross-sectional view ofa present invention hard pellicle/mask assembly 10 is shown. A mask 12is first provided which is constructed by a blank 14 coated with achrome layer 16. The chrome layer 16 is also known as the absorber.After a plurality of spacers 18 are placed on the chrome-coated surfaceof the blank 14, a hard pellicle 20 is mounted to the mask 12 to protectthe chrome layer 16 which forms a pattern of the circuit to bereproduced. In the space 22 between the hard pellicle 20 and the mask 12formed by the plurality of spacers 18, an inert gas that islight-transmitting is used to fill the cavity 22. The light-transmittinggas may be an inert gas selected from N₂, Ar and He. Thelight-transmitting gas normally transmits at least 70% of a light thathas a wavelength smaller than 200 nm. In the preferred and alternateembodiments of the present invention, the light-transmitting gasutilized is N₂.

[0028] An alternate embodiment 30 of the present invention hardpellicle/mask assembly is shown in FIG. 2. Similar to the preferredembodiment 10 shown in FIG. 1, a second plurality of spacers 24 thathave a predetermined thickness is used in-between the mask 12 and thesecond hard pellicle 26. An interior space 28 formed by the second hardpellicle 26 and the mask 12 is similarly filled with alight-transmitting gas of N₂.

[0029] The first hard pellicle 20 and the second hard pellicle 26 haveoptical properties at least that of a quartz lens in order to maintainthe imaging intensity of the imaging system of the scanner. This isshown in FIGS. 3 and 4. It should be noted that in many circumstances, amask 12 may only need a single hard pellicle mounted on thechrome-coating side, or the side with the patterned absorber layer. Thelight-transmitting gas used in the present invention to fill theinterior cavities 22, 28 prevents any light loss due to the presence ofthe gas. As shown in FIGS. 3 and 4, either a mask covered by a singlehard pellicle or a mask covered by two hard pellicles is provided forexposure in the scanner 40. In the pellicle preparation space 50, a mask12 is first disassembled with the protective cover 32 removed and storedin the pellicle preparation space 50. The removal of the protectivecover 32 is accomplished by a demounting means which removes the clamps34 that were used to hold the protective cover onto the mask 12. Themask/protective cover assembly 36 is first transported into the pelliclepreparation space 50 through an input door 38 mounted at one end of thepellicle preparation space 50.

[0030] After the clamps 34 are temporarily removed from the mask 12 andthe protective cover 32 is removed, a hard pellicle 20 with a pluralityof spacers 18 positioned along the edges of the hard pellicle 20 ismounted to the mask 12 and then clamped by the mechanical clamp 34. Thehard pellicle/mask assembly 10 is then transported, through an outputdoor 44 into the scanner 40 for projecting and exposing an image onto asemiconductor wafer 60. A series of imaging lens 46 are used incontrolling the imaging and the exposure process. An optical source 70is utilized in projecting through lens 72 into the hard pellicle/maskassembly 10.

[0031]FIG. 4 shows an alternate embodiment of the present inventionwherein a hard pellicle/mask assembly 30 covered on both sides by hardpellicles 20 and 26 is utilized in place of the hard pellicle/maskassembly 10 shown in FIG. 3.

[0032] The present invention apparatus for mounting at least one hardpellicle to a mask and a projection mask aligner with a hard pelliclepreparation space mounted thereto have therefore been amply described inthe above description and in the appended drawings of FIGS. 1-4.

[0033] While the present invention has been described in an illustrativemanner, it should be understood that the terminology used is intended tobe in a nature of words of description rather than of limitation.

[0034] Furthermore, while the present invention has been described interms of one preferred and one alternate embodiment, it is to beappreciated that those skilled in the art will readily apply theseteachings to other possible variations of the inventions.

[0035] The embodiment of the invention in which an exclusive property orprivilege is claimed are defined as follows.

What is claimed is:
 1. An apparatus for mounting at least one hardpellicle to a mask comprising: an enclosure comprising an interiorcavity sufficiently large to accommodate a mask, an inlet port forreceiving a mask with a protective cover mounted thereon, and an outletport for outputting a mask covered by at least one hard pellicle;demounting means for removing said protective cover from said mask;mounting means for mounting said at least one hard pellicle on said maskforming a hard pellicle/mask assembly; and conduit means for receiving alight-transmitting gas and for filling said interior cavity with saidlight-transmitting gas.
 2. The apparatus for mounting a hard pellicle toa mask according to claim 1 further comprising delivery means fordelivering said at least one hard pellicle covered mask to a scanner. 3.The apparatus for mounting a hard pellicle to a mask according to claim1, wherein said light-transmitting gas is a gas that transmits at least70% of a light having a wavelength smaller than 200 nm.
 4. The apparatusfor mounting a hard pellicle to a mask according to claim 1, whereinsaid light-transmitting gas is an inert gas selected from the groupconsisting of N₂, Ar and He.
 5. The apparatus for mounting a hardpellicle to a mask according to claim 1, wherein said light-transmittinggas is N₂.
 6. The apparatus for mounting a hard pellicle to a maskaccording to claim 1, wherein said mounting means comprises mechanicalclamps.
 7. The apparatus for mounting a hard pellicle to a maskaccording to claim 1, wherein said mounting means mounts a first hardpellicle on said mask juxtaposed to a surface having a layer of chromecoating.
 8. The apparatus for mounting a hard pellicle to a maskaccording to claim 1, wherein said mounting means mounts a second hardpellicle on said mask juxtaposed to a surface opposite to said surfacehaving said layer of chrome coating.
 9. The apparatus for mounting ahard pellicle to a mask according to claim 1, wherein said at least onelight-transmitting gas is an inert gas selected from the groupconsisting of N₂, Ar and He.
 10. The apparatus for mounting a hardpellicle to a mask according to claim 1 further comprising a pluralityof spacers of predetermined thickness mounted in-between said at leastone hard pellicle and said mask.
 11. The apparatus for mounting a hardpellicle to a mask according to claim 1 further comprising hard pelliclestorage means.
 12. The apparatus for mounting a hard pellicle to a maskaccording to claim 1 further comprising mask storage means.
 13. Theapparatus for mounting a hard pellicle to a mask according to claim 1further comprising hard pellicle/mask assembly storage means.
 14. Animproved projection mask aligner of the type in which a mask having aprotective cover mounted thereon is positioned in-between a light sourceand an imaging lens for projecting an image on a photoresist coatedsemiconductor wafer in order to form microelectronic circuits on saidsemiconductor wafer, wherein the improvement comprises: a hard pelliclemounting apparatus positioned juxtaposed to said projection mask alignerfor delivering a hard pellicle/mask assembly into said projection maskaligner, said hard pellicle mounting apparatus comprises an enclosurehaving an interior cavity sufficiently large to accommodate a mask, aninlet port for receiving a mask with a protective cover mounted thereon,and an outlet port for outputting a mask covered by at least one hardpellicle; demounting means for removing said protective cover from saidmask; mounting means for mounting said at least one hard pellicle onsaid mask forming a hard pellicle/mask assembly; and conduit means forreceiving a light-transmitting gas and for filling said interior cavitywith said light-transmitting gas.
 15. The improved projection maskaligner according to claim 14 further comprising a delivery means fordelivering said hard pellicle/mask assembly into said projection maskaligner.
 16. The improved projection mask aligner according to claim 14,wherein said light-transmitting gas is a gas that transmits at least 70%of a light having a wavelength smaller than 200 nm.
 17. The improvedprojection mask aligner according to claim 14, wherein said mountingmeans comprises mechanical clamps.
 18. The improved projection maskaligner according to claim 14, wherein said light-transmitting gas is aninert gas selected from the group consisting of N₂, Ar and He.
 19. Theimproved projection mask aligner according to claim 14, wherein said atleast one hard pellicle having optical properties at least that of aquartz lens.
 20. The improved projection mask aligner according to claim14 further comprising a plurality of spacers of predetermined thicknessmounted in-between said at least one hard pellicle and said mask.
 21. Amethod for imaging wafers using a projection mask aligner comprising thesteps of: providing a projection mask aligner equipped with a hardpellicle mounting apparatus, said hard pellicle mounting apparatusfurther comprises an enclosure comprising an interior cavitysufficiently large to accommodate a mask, an inlet port for receiving amask with a protective cover mounted thereon, and an outlet port foroutputting a mask covered by at least one hard pellicle; demountingmeans for removing said protective cover from said mask; mounting meansfor mounting said at least one hard pellicle on said mask forming a hardpellicle/mask assembly; and conduit means for receiving alight-transmitting gas; forming a hard pellicle/mask assembly having atleast one hard pellicle mounted thereon; positioning said hardpellicle/mask assembly in-between a light source and an imaging lens;positioning a photoresist coated semiconductor wafer under said imaginglens with a photoresist layer facing said lens; and imagingmicroelectronic circuits on said hard pellicle/mask assembly onto saidsemiconductor wafer.
 22. The method for imaging wafers using aprojection mask aligner according to claim 21 further comprising thestep of flowing a light-transmitting gas into and filling said interiorcavity of said enclosure.
 23. The method for imaging wafers using aprojection mask aligner according to claim 21 further comprising thestep of forming said hard pellicle/mask assembly by clamping at leastone pellicle to said mask by mechanical means.
 24. The method forimaging wafers using a projection mask aligner according to claim 21further comprising the step of supplying said at least one hard pelliclein a material having optical properties at least that of quartz.
 25. Themethod for imaging wafers using a projection mask aligner according toclaim 21 further comprising the step of storing said at least one hardpellicle in said hard pellicle mounting apparatus.